Zoom lens system in finite conjugate distance

ABSTRACT

With a stop disposed at the center, a lens system are composed of four sheets of positive, negative, negative, and positive lenses. At the time of variable magnification, the whole lens system is moved while distances between the lenses are changed, whereby a low cost and a compact size are attained in a zoom lens system for copying. This lens system is constituted by four sheets of positive, negative, negative, and positive lenses (L 1  to L 4 ) which are disposed in pairs laterally symmetrical to each other with respect to the stop. At the time of reducing or enlarging, the distance between the first lens (L 1 ) and second lens (L 2 ), the distance between the third lens (L 3 ) and fourth lens (L 4 ), and the distance between the second lens (L 2 ) and third lens (L 3 ) are made larger than those under real-size magnification, while the whole system is moved with the distance from the object surface to the imaging surface being held substantially constant so as to attain variable power.

RELATED APPLICATIONS

This application claims the priority of Japanese Patent Application No.7-286873 filed on Oct. 6, 1995, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens system in a finiteconjugate distance, which is suitable for copying under near real-sizemagnification in a copying machine, a photomechanical processor, or thelike and, in particular, to a zoom lens system composed of four sheetsof lenses in which the distance from the object surface to the imagingsurface does not change even at the time of variable magnification.

2. Description of the Prior Art

As a zoom lens system suitable for copying under near real-sizemagnification which is used in a copying machine, a photomechanicalprocessor, or the like, there have conventionally been known zoom lenssystems in which the distance from the object surface to the imagingsurface does not change even at the time of variable magnification.

As this kind of lenses, those disclosed in Japanese Unexamined PatentPublication No. 62-180317 (Japanese Patent Publication No. 7-1338) andJapanese Unexamined Patent Publication No. 59-61814 have been known.

Of the above-mentioned conventional lenses, however, the former andlatter are respectively composed of five and six sheets of lenses, andthere has been a demand for a copying zoom lens composed of four sheetsof lenses in order to attain a low cost and a compact size.

SUMMARY OF THE INVENTION

In view of such a circumstance, the object of the present invention isto provide a zoom lens system in a finite conjugate distance, in whichthe distance from the object surface to the imaging surface does notchange even at the time of variable magnification, and which is suitablefor copying under near real-size magnification, yields a highperformance, while attaining a low cost and a compact size.

The zoom lens system in a finite conjugate distance in accordance withthe present invention comprises, successively from the object side, afirst lens comprising a biconvex lens, a second lens comprising abiconcave lens, a third lens comprising a biconcave lens, and a fourthlens comprising a biconvex lens;

wherein, distance between the first lens and second lens, distancebetween the third lens and fourth lens, and distance between the secondlens and third lens when the imaging magnification is reduced orenlarged are made larger than those under real-size magnification, andwherein the whole system is moved while the distance from the objectsurface to the imaging surface is held substantially constant whenmagnification is varied.

Also, more desirably, the zoom lens system is configured so as tosatisfy the following conditional expressions (1) to (5):

    (1) 0.27<|f.sub.1 |/f<0.40

    (2) 0.30<|f.sub.2 |/f<0.44

    (3) 0.40<(Δd.sub.2 +Δd.sub.6)/Δd.sub.4 <2.50

    (4) 0.40<Δd.sub.2 /Δd.sub.6 <1.10 (when |β|≧1)

    (5) 0.90<Δd.sub.2 /Δd.sub.6 <1.70 (when |β|<1)

wherein

f is focal length of the whole system when magnification is -1.0;

f₁ is focal length of the first lens;

f₂ is focal length of the second lens;

β is magnification;

Δd₂ is (distance between the first lens and second lens whenmagnification β is β_(x))-(distance between the first lens and secondlens when magnification β is -1);

Δd₄ is (distance between the second lens and third lens whenmagnification β is β_(x))-(distance between the second lens and thirdlens when magnification - is -1); and

Δd₆ is (distance between the third lens and fourth lens whenmagnification β is β_(x))-(distance between the third lens and fourthlens when magnification β is -1).

More specifically, for example, assuming that the lens surfaces aresuccessively counted from the object side, it is desirable that theabsolute values of radii of curvature of the first, second, third, andfourth lens surfaces be respectively identical to those of the eighth,seventh, sixth, and fifth lens surfaces, and that the center thicknessvalues of the first and second lenses as well as refractive index valuesof their materials be respectively identical to those of the fourth andthird lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a basic lens configuration inaccordance with Embodiments 1 to 8 of the present invention;

FIG. 2 is an aberration chart of the lens in accordance with Embodiment1 (β=-1.224);

FIG. 3 is an aberration chart of the lens in accordance with Embodiment1 (β=-1.0);

FIG. 4 is an aberration chart of the lens in accordance with Embodiment1 (β=-0.707);

FIG. 5 is an aberration chart of the lens in accordance with Embodiment2 (β=-1.414);

FIG. 6 is an aberration chart of the lens in accordance with Embodiment2 (β=-1.0);

FIG. 7 is an aberration chart of the lens in accordance with Embodiment2 (β=-0.707);

FIG. 8 is an aberration chart of the lens in accordance with Embodiment3 (β=-1.414);

FIG. 9 is an aberration chart of the lens in accordance with Embodiment3 (β=-1.0);

FIG. 10 is an aberration chart of the lens in accordance with Embodiment3 (β=-0.707);

FIG. 11 is an aberration chart of the lens in accordance with Embodiment4 (β=-1.414);

FIG. 12 is an aberration chart of the lens in accordance with Embodiment4 (β=-1.0);

FIG. 13 is an aberration chart of the lens in accordance with Embodiment4 (β=-0.707);

FIG. 14 is an aberration chart of the lens in accordance with Embodiment5 (β=-1.414);

FIG. 15 is an aberration chart of the lens in accordance with Embodiment5 (β=-1.0);

FIG. 16 is an aberration chart of the lens in accordance with Embodiment5 (β=-0.707);

FIG. 17 is an aberration chart of the lens in accordance with Embodiment6 (β=-2.0);

FIG. 18 is an aberration chart of the lens in accordance with Embodiment6 (β=-1.0);

FIG. 19 is an aberration chart of the lens in accordance with Embodiment6 (β=-0.5);

FIG. 20 is an aberration chart of the lens in accordance with Embodiment7 (β=-1.414);

FIG. 21 is an aberration chart of the lens in accordance with Embodiment7 (β=-1.0);

FIG. 22 is an aberration chart of the lens in accordance with Embodiment7 (β=-0.707);

FIG. 23 is an aberration chart of the lens in accordance with Embodiment8 (β=-1.414);

FIG. 24 is an aberration chart of the lens in accordance with Embodiment8 (β=-1.0); and

FIG. 25 is an aberration chart of the lens in accordance with Embodiment8 (β=-0.707).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be explainedwith reference to drawings.

Here, FIG. 1 shows a basic lens configuration of Embodiments 1 to 8. Asshown in FIG. 1, the lens system in accordance with these embodiments isconstituted by four sheets of lenses L₁ to L₄ which are disposed inpairs symmetrical to each other with respect to a stop i, and a luminousflux incident on the lens system from the object side along an opticalaxis X forms an image at an imaging position P.

Here, the first lens L₁ is a biconvex lens having a surface with alarger curvature directed onto the object side, the second lens L₂ is abiconcave lens having a surface with a larger curvature directed ontothe imaging surface side (except for Embodiment 1 wherein a surface witha weaker curvature is directed onto the imaging surface side), the thirdlens L₃ is a biconcave lens whose direction is opposite to that of thesecond lens L₂, and the fourth lens L₄ is a biconvex lens whosedirection is opposite to that of the first lens L₁.

Namely, assuming that the lens surfaces are successively counted fromthe object side, the absolute values of radii of curvature of the first,second, third, and fourth lens surfaces are respectively identical tothose of the eighth, seventh, sixth, and fifth lens surfaces. Also, thecenter thickness values of the first and second lenses as well as theirmaterials (refractive index values) are respectively identical to thoseof the fourth and third lenses.

Also, this lens system is configured such that distance between thefirst lens and second lens, distance between the third lens and fourthlens, and distance between the second lens and third lens when theimaging magnification is reduced or enlarged are made larger than thoseunder real-size magnification, whereas the whole system is moved withthe distance from the object surface to the imaging surface being heldsubstantially constant when magnification is varied. Also, the lenssystem is configured so as to satisfy the following conditionalexpressions (1) to (5):

    (1) 0.27<|f.sub.1 |/f<0.40

    (2) 0.30<|f.sub.2 |/f<0.44

    (3) 0.40<(Δd.sub.2 +Δd.sub.6)Δd.sub.4 <2.50

    (4) 0.40<Δd.sub.2 /Δd.sub.6 <1.10 (when |β|≧1)

    (5) 0.90<Δd.sub.2 /Δd.sub.6 <1.70 (when |β|<1)

wherein

f is focal length of the whole system when magnification is -1.0;

f₁ is focal length of the first lens;

f₂ is focal length of the second lens;

β is magnification;

Δd₂ is (distance between the first lens and second lens whenmagnification β is β_(x))-(distance between the first lens and secondlens when magnification β is -1);

d₄ is (distance between the second lens and third lens whenmagnification β is β_(x))-(distance between the second lens and thirdlens when magnification β is -1); and

Δd₆ is (distance between the third lens and fourth lens whenmagnification β is β_(x))-(distance between the third lens and fourthlens when magnification β is -1).

In the following, technical significance of each of the above-mentionedexpressions (1) to (5) will be explained. Namely, conditionalexpressions (1) and (2) have similar significance. Below their lowerlimits, spherical aberration is corrected too much, while a higheraccuracy is required for lens spacing such that it becomes difficult tomanufacture the lens system. Above their upper limits, by contrast,spherical aberration is corrected insufficiently, whereby favorableimaging performance may not be obtained.

Below the lower limit of conditional expression (3), the image surfacecurvature becomes larger on the lens side. Above its upper limit, bycontrast, the image surface curvature becomes larger on the sideopposite to the lens, whereby a favorable imaging performance may not beobtained in the whole image surface area.

Below the lower limit of conditional expression (4), coma is correctedtoo much under enlarging magnification, thereby increasing distortion.Above its upper limit, by contrast, coma is corrected insufficiently. Inany of these cases, a favorable imaging performance may not be obtained.

Below the lower limit of conditional expression (5), coma is correctedinsufficiently under reducing magnification. Above its upper limit, bycontrast, coma is corrected too much, while distortion is increased. Asa result, in any of these cases, a favorable imaging performance may notbe obtained.

In the following, Embodiments 1 to 8 will be explained with reference totheir specific values.

Embodiment 1

Table 1 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.224and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d-line inEmbodiment 1.

Also, the middle portion of Table 1 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-1.224 , β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 1 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment. Embodiment 2

Table 2 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d-line inEmbodiment 2.

Also, the middle portion of Table 2 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-1.414 , β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 2 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 3

Table 3 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d- line inEmbodiment 3.

Also, the middle portion of Table 3 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle 107 (wherein β=-1.414, β=-1.0, and β=-0.707) of the wholelens system in accordance with this embodiment.

Further, the lower portion of Table 3 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 4

Table 4 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d-line inEmbodiment 4.

Also, the middle portion of Table 4 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and haftfield angle ω(wherein β=-1.414, β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 4 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 5

Table 5 (follows) shows radius of curvature r (mm) of each lens surfacecenter thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d- line inEmbodiment 5.

Also, the middle portion of Table 5 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-1.414, β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 5 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 6

Table 6 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-2.0and β=-0.5 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d-line inEmbodiment 6.

Also, the middle portion of Table 6 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-2.0, β=-1.0, and β=-0.5) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 6 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 7

Table 7 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d- line inEmbodiment 7.

Also, the middle portion of Table 7 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-1.414, β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 7 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

Embodiment 8

Table 8 (follows) shows radius of curvature r (mm) of each lens surface,center thickness of each lens and air gap between neighboring lenses d(mm)(wherein imaging magnification β=-1.0; whereas the cases of β=-1.414and β=-0.707 are also shown for variable distances d₂, d₄, and d₆), andrefractive index N and Abbe number ν of each lens at d-line inEmbodiment 8.

Also, the middle portion of Table 8 shows the respective values of focallength f (wherein imaging magnification β=-1.0), F number, and halffield angle ω(wherein β=-1.414, β=-1.0, and β=-0.707) of the whole lenssystem in accordance with this embodiment.

Further, the lower portion of Table 8 shows values respectivelycorresponding to the above-mentioned conditional expressions (1) to (5)in this embodiment.

FIGS. 2 to 25 show aberration charts of Embodiments 1 to 8 (with three βvalues for each embodiment).

As can be seen from these charts, in accordance with these embodiments,various kinds of aberration can be made favorable not only at the timeof real-size magnification but also at the time of enlarging andreducing.

Without being restricted to the foregoing embodiments, the lens systemof the present invention can be modified in various manners. Forexample, the radius of curvature r and lens spacing (or lens thickness)d in each of four sheets of lenses can be appropriately changed.

As explained in the foregoing, in the zoom lens system in a finiteconjugate distance in accordance with the present invention, positive,negative, negative, and positive lenses are successively disposed fromthe object side and, at the time of reducing and enlarging, the wholelens system is moved with the distance from the object surface to theimaging surface being held constant, while the distances between theconstitutional lenses are changed so as to become larger than those atthe time of real-size magnification. Accordingly, a high-performancezoom lens system suitable for copying under near real-sizemagnification, which can favorably correct various kinds of aberration,while being composed of four sheets of lenses, is formed.

Therefore, as compared with conventional lens systems, a lowermanufacturing cost and a more compact size in the whole lens system canbe attained.

                  TABLE 1                                                         ______________________________________                                        Surface                 d                                                     No.   r       β = -1.224                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     31.264            5.391         1.62041                                                                             60.3                              2     -89.946 2.955     2.868 3.366                                           3     -42.155           1.332         1.53256                                                                             46.0                              4     47.505  2.793     2.604 2.966                                           5     -47.505           1.332         1.53256                                                                             46.0                              6     42.155  3.064     2.868 3.205                                           7     89.946            5.391         1.62041                                                                             60.3                              8     -31.264                                                                 f = 100 (β = -1.0), F/NO = 5.6                                           Half field angle ω = 16.0° (β = -1.224)                     Half field angle ω = 17.5° (β = -1.0)                       Half field angle ω = 15.1° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.380                                        |f.sub.2 |/f = 0.417                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 1.494 (β =            -1.224)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 2.303 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.441 (β = -1.224)                     (Δd.sub.2 /Δd.sub.6 = 1.479 (β = -0.707)                     ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Surface                 d                                                     No.   r       β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     27.810            5.008         1.62280                                                                             56.9                              2     -58.097 1.335     1.114 1.390                                           3     -38.526           1.168         1.54869                                                                             45.4                              4     34.756  4.239     3.075 4.075                                           5     -34.756           1.168         1.54869                                                                             45.4                              6     38.526  1.395     1.114 1.334                                           7     58.097            5.008         1.62280                                                                             56.9                              8     -27.810                                                                 f = 100 (β = -1.0), F/NO = 8                                             Half field angle ω = 19.0° (β = -1.414)                     Half field angle ω = 22.0° (β = -1.0)                       Half field angle ω = 19.0° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.309                                        |f.sub.2 |/f = 0.331                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.431 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.496 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.788 (β = -1.414)                     (Δd.sub.2 /Δd.sub.6 = 1.251 (β = -0.707)                     ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Surface                 d                                                     No.   r       β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     26.574            3.945         1.62299                                                                             58.1                              2     -57.470 1.331     1.107 1.328                                           3     -38.161           1.813         1.54072                                                                             47.2                              4     31.521  3.423     2.404 3.227                                           5     -31.521           1.813         1.54072                                                                             47.2                              6     38.161  1.331     1.107 1.328                                           7     57.470            3.945         1.62299                                                                             58.1                              8     -26.574                                                                 f = 100 (β = -1.0), F/NO = 8                                             Half field angle ω = 16.8° (β = -1.414)                     Half field angle ω = 19.5° (β = -1.0)                       Half field angle ω = 16.8° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.297                                        |f.sub.2 |/f = 0.316                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.439 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.536 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 1.0 (β = -1.414)                       (Δd.sub.2 /Δd.sub.6 = 1.0 (β = -0.707)                       ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Surface                 d                                                     No.   r       β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     24.433            2.896         1.62299                                                                             58.1                              2     -66.338 1.280     1.116 1.355                                           3     -39.739           0.895         1.54072                                                                             47.2                              4     29.768  3.911     3.265 3.791                                           5     -29.768           0.895         1.54072                                                                             47.2                              6     39.739  1.358     1.116 1.280                                           7     66.338            2.896         1.62299                                                                             58.1                              8     -24.433                                                                 f = 100 (β = -1.0), F/NO = 8                                             Half field angle ω = 18.4° (β = -1.414)                     Half field angle ω = 21.4° (β = -1.0)                       Half field angle ω = 18.4° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.290                                        |f.sub.2 |/f = 0.313                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.628 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.765 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.678 (β = -1.414)                     (Δd.sub.2 /Δd.sub.6 = 1.456 (β = -0.707)                     ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Surface                 d                                                     No.   r       β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     24.148            2.946         1.62299                                                                             58.1                              2     -69.583 1.338     1.182 1.425                                           3     -39.730           0.882         1.54072                                                                             47.2                              4     29.835  3.215     2.752 3.096                                           5     -29.835           0.882         1.54072                                                                             47.2                              6     39.730  1.428     1.182 1.338                                           7     69.583            2.946         1.62299                                                                             58.1                              8     -24.148                                                                 f = 100 (β = -1.0), F/NO = 8                                             Half field angle ω = 17.9° (β = -1.414)                     Half field angle ω = 20.7° (β = -1.0)                       Half field angle ω = 17.9° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.291                                        |f.sub.2 |/f = 0.314                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.869 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 1.158 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.632 (β = -1.414)                     (Δd.sub.2 /Δd.sub.6 = 1.552 (β = -0.707)                     ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Surface                 d             N     ν                              No.   r       β = -2.0                                                                           β = -1.0                                                                       β = -0.5                                   ______________________________________                                        1     23.404            2.234         1.62299                                                                             58.1                              2     -75.154 2.210     1.370 2.201                                           3     -39.957           0.846         1.54072                                                                             47.2                              4     29.389  4.621     3.009 4.281                                           5     -29.389           0.846         1.54072                                                                             47.2                              6     39.957  2.210     1.370 2.201                                           7     75.154            2.234         1.62299                                                                             58.1                              8     -23.404                                                                 f = 100 (β = -1.0), F/NO = 10                                            Half field angle ω = 15.8° (β = -2.0)                       Half field angle ω = 20.7° (β = -1.0)                       Half field angle ω = 15.8° (β = -0.5)                       Values of expression                                                          |f.sub.1 |/f = 0.289                                        |f.sub.2 |/f = 0.312                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 1.042 (β = -2.0)      (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 1.310 (β = -0.5)      (Δd.sub.2 /Δd.sub.6 = 1.0 (β = -2.0)                         (Δd.sub.2 /Δd.sub.6 = 1.0 (β = -0.5)                         ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Surface                 d                                                     No.           β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     26.912            5.044         1.60311                                                                             60.7                              2     -55.789 1.354     1.136 1.406                                           3     -36.805           1.083         1.53172                                                                             48.9                              4     33.792  3.667     2.599 3.511                                           5     -33.792           1.083         1.53172                                                                             48.9                              6     36.805  1.411     1.136 1.353                                           7     55.789            5.044         1.60311                                                                             60.7                              8     -26.912                                                                 f = 100 (β = -1.0), F/NO = 8                                             Half field angle ω = 18.5° (β = -1.414)                     Half field angle ω = 21.4° (β = -1.0)                       Half field angle ω = 18.5° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.308                                        |f.sub.2 |/f = 0.330                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.462 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.535 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.792 (β = -1.414)                     (Δd.sub.2 /Δd.sub.6 = 1.245 (β = -0.707)                     ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Surface                 d                                                     No.           β = -1.414                                                                         β = -1.0                                                                       β = -0.707                                                                       N     ν                              ______________________________________                                        1     28.153            4.323         1.65844                                                                             50.8                              2     -70.856 1.473     1.267 1.551                                           3     -43.092           1.436         1.58144                                                                             40.8                              4     35.844  3.657     2.872 3.518                                           5     -35.844           1.436         1.58144                                                                             40.8                              6     43.092  1.556     1.267 1.473                                           7     70.856            4.323         1.65844                                                                             50.8                              8     -28.153                                                                 f = 100 (β = -1.0), F/NO = 6.3                                           Half field angle ω = 18.5° (β = -1.414)                     Half field angle ω = 21.4° (β = -1.0)                       Half field angle ω = 18.5° (β = -0.707)                     Values of expression                                                          |f.sub.1 |/f = 0.311                                        |f.sub.2 |/f = 0.335                                        (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.631 (β =            -1.414)                                                                       (Δd.sub.2 + Δd.sub.6)/Δd.sub.4 = 0.759 (β =            -0.707)                                                                       (Δd.sub.2 /Δd.sub.6 = 0.714 (β = -1.414)                     (Δd.sub.2 /Δd.sub.6 = 1.378 (β = -0.707)                     ______________________________________                                    

What is claimed is:
 1. A zoom lens system in a finite conjugatedistance, said zoom lens system comprising, successively from an objectside, a first lens comprising a biconvex lens, a second lens comprisinga biconcave lens, a third lens comprising a biconcave lens, and a fourthlens comprising a biconvex lens;wherein, distance between said firstlens and second lens, distance between said third lens and fourth lens,and distance between said second lens and third lens when imagingmagnification is reduced or enlarged are made larger than those underreal-size magnification, and wherein the whole system is moved whiledistance from an object surface to an imaging surface is heldsubstantially constant when magnification is varied.
 2. A zoom lenssystem in a finite conjugate distance according to claim 1, wherein saidlens system is configured so as to satisfy the following conditionalexpressions (1) to (5):

    (1) 0.27<|f.sub.1 |/f<0.40

    (2) 0.30<|f.sub.2 |/f<0.44

    (3) 0.40<(Δd.sub.2 +Δd.sub.6)/Δd.sub.4 <2.50

    (4) 0.40<Δd.sub.2 /Δd.sub.6 <1.10(when |β|≧1)

    (5) 0.90<Δd.sub.2 /Δd.sub.6 <1.70(when |β|<1)

wherein f is focal length of the whole system when magnification is-1.0; f₁ is focal length of the first lens; f₂ is focal length of thesecond lens; β is magnification; Δd₂ is (distance between the first lensand second lens when magnification β is β_(x))-(distance between thefirst lens and second lens when magnification β is -1); Δd₄ is (distancebetween the second lens and third lens when magnification β isβ_(x))-(distance between the second lens and third lens whenmagnification β is -1); and Δd₆ is (distance between the third lens andfourth lens when magnification β is β_(x))-(distance between the thirdlens and fourth lens when magnification β is -1).
 3. A zoom lens systemin a finite conjugate distance according to claim 2, wherein assumingthat lens surfaces are successively counted from the object side,absolute values of radii of curvature of first, second, third, andfourth lens surfaces are respectively identical to those of eighth,seventh, sixth, and fifth lens surfaces, and wherein center thicknessvalues of said first and second lenses as well as refractive indexvalues of materials thereof are respectively identical to those of saidfourth and third lenses.